This invention relates to an image pickup device, and more particularly to an image pickup device suitable for dimensional measurement.
As an example of the conventional image pickup device, the pixel arrangement in an image pickup device 1 such as a CCD (charge coupled device) line image sensor, etc. is shown in FIG. 1. As seen from this figure, pixels 3 are arranged in a row at a pitch P to constitute a pixel train 2. An image of an object to be measured is formed on the arrangement of the pixel train 2 to carry out photoelectric conversion, thus to provide image information.
However, in the case of such an image pickup device 1, the resolution thereof is determined by the pitch P of the pixels 3. As a result, the measurement accuracy is restricted by the length of the pitch P. If the pitch P is caused to be small, the resolution becomes high, but there is a limit in production. In general, the minimum pitch P of the pixels 3 put into practice is 7 .mu.m. Resolution more than that value can not be provided.
Furthermore, if the dimension or size of the pixel 3 becomes small, the quantity of charges which can be stored is decreased, leading to a lowered SN ratio (hereinafter simply referred to S/N). Accordingly, it is extremely difficult to increase the resolution of the image pickup device 1 for improving the measurement accuracy.